In an ordinary vehicle, for closing a door such as a trunk lid, for example, a latch is provided on the trunk lid, while a striker is provided on a body of the vehicle, so that the door is closed such that the latch and the striker are engaged with each other.
In the vehicle, for example, when the trunk lid is closed, the trunk lid must be pushed toward the body, while a weather strip provided on the body of the vehicle is being deformed elastically, that results in increase of a force required for closing the trunk lid. Accordingly, when the trunk lid is closed, it must be forcibly pushed down. Since vibrations at a closing time of the door become large, a rear seat passenger or vehicle occupant may feel uncomfortable. In view of these circumstances, especially, in some of high class vehicles, a door closer provided with a door-closing assisting mechanism that pulls in a striker engaged with a latch and a driving apparatus that actuates the door-closing assisting mechanism. The driving apparatus is usually provided with a driving motor (a driving source), a worm (a driving gear) provided on a rotational shaft of the driving motor, and a worm wheel (a driven gear) that is engaged with the worm (see, for example, Japanese Registered Utility Model Publication No. 2562770 (pages 2 to 4, FIG. 6)).
In a vehicle on which the door closer is mounted, since a trunk lid can be closed by a rotation of the worm wheel performed by driving of the driving motor, vibrations due to forcible pushing-down of the trunk lid at a closing time of the trunk lid are not generated.
As described above, since a large force is required to close the trunk lid, a large-sized driving motor generating large power is used as the driving motor in the driving apparatus.
Therefore, since power transmitted from the driving motor to the worm wheel through the worm inevitably becomes large, a large-sized worm wheel is required for securing a sufficient strength as the worm wheel, which results in over-sizing of the driving apparatus and a door closer including the driving apparatus.
Accordingly, an object of the present invention is to provide a driving apparatus and a door closer that allow downsizing.